(1) Field of the Invention
The subject of the invention is the plant size production of a better quality, marketable short cooking time rice by decreasing time, work and energy demand significantly by using microwave technology. The process decreases the loss of nutritional value, it consists only of a few, well adjustable steps and is environment friendly.
(2) Prior Art
Rice is one of the most important foods in the world and one of the basic elements of human nourishment which contains valuable carbon hydrates, proteins, mineral salts and vitamins. Rice is the main food of approximately 60% of the Earth's population.
Approximately 90% of rice is grown in Asia and is consumed there as well. Rice as half water, annual grass can be raised under very different climatic conditions.
Generally consumable white rice can be cooked with the usual kitchen techniques in about 20 minutes, but cooking time must be strictly kept, otherwise rice becomes overcooked or in the opposite, it remains raw. Rice absorbs heat and water during cooking. During the long cooking time besides the decrease of enjoyment value quality deterioration, occurs as well, because some of the valuable soluble components dissolve in boiling water and from the nourishment view they are lost. These standpoints played an important role—besides the speeding up of life—in the appearance of fast and half cooked rice products in the market and in the development of manufacturing procedures necessary for the production of above. As a result of this the popularity of more expensive, so-called “pretreated or precooked” short cooking time fast rice products increases more and more. Furthermore precooking makes it possible that some of the nutriments wander to the inside part of rice before burying.
The commercially available “pretreated or precooked” rice products can be divided into three groups:                parboiling rice        instant, ready to eat rice        quick cooking rice        
These rice products have different nutrition values, characteristics, and are cooked with different kitchen technologies and the traditional consumer circle is also different. Historically the first pretreated rice product was parboiling rice, more manufacturing procedures were developed for its production. All other precooking methods originate from the classic parboiling process.
Parboiling Rice
The routes of precooking go back to ancient India, where the gathered, raw, rough rice was soaked during one night in water and on the following day was dried on the sun. After drying the hull of rice cracked, so it was very easy to husk it and use it as food. This ancient method was brought to perfection during the industrial manufacturing of parboiling rice, realizing those advantages which the pretreatment process offers.
These are the following:                the valuable nutriments wander to the endosperm part of rice and thus they are kept        because of the starting gelatinization the grain becomes hard and during hulling the 15 number of broken grain decreases, thus the value of use increases        lipase becomes inactivated in the hull of rice and it increases non-perishability significantly        cooking characteristics of rice become better, it doesn't become sticky        
The basic aim of precooking is to bring rice into a consumable, hulled form. With precooking it is easier to remove the hull. So at the parboiling method the main target is to remove grain hull easily and the precooking of rice is only a by effect.
Numerous patented ways of parboiling pretreatment were invented during the years, which aimed the easier, simpler, more energy saving and more effective solution of production methods.
U.S. Pat. No. 5,017,395 is about the production of a high stability precooked rice. In the soaking step the moisture content of rice is increased to 43-49 m %, and after that it is cooked for 1-10 minutes. Dehydrating is done in two steps, delicately, the first step is drying when the moisture content of rice is decreased to 25-35 m % and after that rice is tempered on 38-66° C. at least for 2 hours for approximately 6 hours and finally dried.
During tempering the starch content of rice becomes fully gelatinized. The so processed rice—because of the slow drying and dehydrating procedure—becomes free from tension, the possibility of breaking, damaging of rice grains is eliminated.
U.S. Pat. No. 5,316,783 aims the production of better quality precooked rice, by keeping the preferable characteristics of already known processes and of the so manufactured products. According to this method the colouration that occurs generally during the heat treatment of rice (Maillard browning effect) is prevented, furthermore the taste of rice will also be better. During preparation rice is soaked on 70° C. for 90 minutes, and the unnecessary water is removed. After that rice is treated with 190° C. hot air for 20 minutes or under pressure with steam for 20 seconds. On basis of comparative experiments it can be determined that the rice processed with this patent method became fully gelatinized and its substance is better, it doesn't contain stuck or damaged, broken grains. Its taste and colour is also more favourable than of the earlier known products.
U.S. Pat. No. 5,130,153 is about the production of precooked rice in more steps. Rice is treated, soaked in water on 50-95° C. until its moisture content reaches 17-28 m %, and then it is steamed on 100-125° C., its moisture content is further increased, then kept under pressure for 1-5 minutes, and after decompression the moisture content of rice is decreased to 24 m % during approximately 1 hour. After that rice is dried until it reaches the microbiologically stable state, approximately 8-10 m % moisture content. For heating and cooking microwave technology can also be used. According to the process the cooking of pre-soaked rice is carried out under 2-4 bar pressure on 135° C. Heating is done preferably with microwave radiation. After cooking the pressure is decreased to an atmospheric level and rice is dried. Moisture content is adjusted to 13 m % by post-drying. This method requires relatively few heat and energy. The so processed product doesn't change colour and fulfils consumer demands better. The patent also covers the machine which is used for precooking.
Hungarian patent no. 200.667 is about the production of precooked rice. The rough rice is soaked, then treated hydrothermally, then dried and polished. The essence of the invention is that rough rice is treated with microwaves on 100° C. for 1-15 minutes, after that unnecessary water is removed and the required 15-20 m % moisture content is adjusted with further microwave treatment.
U.S. Pat. No. 4,810,511 outlines a more-step process on precooking of rice. In the first step rice is soaked in 40-70° C. water for 3.5-5 hours until reaching 26-32 m % moisture content. After that rice is put through a microwave radiation, pretreatment on 95-100° C. when the moisture content is increased to 40 m % and the gelatinization of starch begins. After removing the unnecessary water rice is treated with a second microwave radiation on 90-110° C. for at least 120 minutes. In this phase the starch content becomes fully gelatinized and the moisture content decreased to 22 m %. Finally the moisture content of. rice is adjusted to 14 m % with hot air drying. The microwave treatment is carried out with electromagnetic radiation of 1-300 m wavelength, frequency 915-22125 mHz. The energy requirement of the process is very small because after the second microwave treatment the moisture content of the products can be decreased to 23-25 m %. The energy of drying can further be cut if the second microwave treatment is done in a hot air stream.
Parboiling treatment—besides its undisputable advantages—also has drawbacks: and it is the change of colour to yellow. Rice consuming eating culture is very different in the world, and in many places snow-white colour of rice is a requirement. The yellow perhaps brown colour of parboiling rice is caused by the products of Maillard reaction which take place during heat transmission steps. Parboiling rice is usually ready in 20 minutes—perhaps a little longer—it is not so sensitive to overcooking. This time is still quite long, so further research was done on reducing cooking time. This target was reached with additional heat treatment, as a result of which fast or quick cooking time rice products were won.
Quick Cooking Rice
Quick cooking rice offers a fast and comfortable kitchen technology solution as it can be cooked in 5-10 minutes and the short cooking time can be kept precisely, thus generally good quality, good looking rice garnishment can be made. At the same time the pretreated, microbiologically stable quick cooking rice can be stored practically for an unlimited time.
In case of quick cooking time it is an important requirement that at the end of cooking time we get same cooked, non-sticky, whole and regular formed rice. These conditions are not easy to fulfill at the same time, several methods were developed to reach the appropriate quality.
The classic quick cooking process follows the parboiling method step by step with the difference that the level of cooking, i.e. the value of gelatinized starch reaches 80-90%. Because of perishableness the water content of grains have to be readjusted to 12-14 m %. In case of quick cooking rice the main target is the proper precooking and re-drying to a microbiologically stable moisture content on 20° C. These two processes are very important because past-cooking time and porosity of rice grains depends on them, which determine the quality of directly consumable rice. After that the ready to eat rice can be cooked from the prepared rice in less than 10 minutes.
For making quick cooking rice, the following is a typical and optimal process according to U.S. Pat. No. 5,089,281:                usual soaking step on 50-70° C.        after a two step cooking process moisture is 60-65%, gelatinization is 80-90%.                    water precooking with 1:2 rice water ration 2.5 minutes, 100° C.            steam cooking: following water cooking 5.5 minutes, 1.5 atm                        after two step drying process moisture is 8%, gelatinization is 100%                    conveyor, hot air drying 7 minutes 150° C.            fluid bed drying 1 minutes 150° C.                        
The procedure is suitable to produce quick cooking, hulled, white rice, parboiling rice and brown rice. The so manufactured rice is consumable after 5-10 minutes kitchen cooking. Rice can also be cooked with microwave oven for 2-20 minutes.
U.S. Pat. No. 4,233,327 writes down quick cooking rice cooking process. At the generally used soaking step 0.1-1 m % tenside e.g. oil is added to the water. During cooking the whole starch content of rice is gelatinized, and then water content is reduced in two steps in a hot air stream. When reaching 25 m % moisture content rice is let to rest on 15-35° C. for at least 30 minutes. The delicate drying method and the use of low temperature prevents the breaking of grains. You only have to pour hot water on the so prepared rice and after a few minutes it can be served.
U.S. Pat. No. 4,548,830 is about the production of rice mush. The washed rice is cooked in more steps in salted water, steamed under pressure and dried with air on microwave treatment until 12-13 m % moisture content is reached.
U.S. Pat. No. 4,794,012 writes down the production of dried, partly gelatinized rice. Rice is first soaked in water under 30° C. for 1-16 hours, then further soaking is done in water with higher temperature, 50-70° C. for another 30-90 minutes. The cooking of rice is carried out with 95-100° C. steam for 5-30 minutes. Drying is done with hot air stream on 60-140° C. for 20-100 minutes or under pressure with 200-400° C. air for 7-30 seconds. The so processed product can be prepared to eat in a short time, its substance is rolling, and the grains don't stick to each other.
The novelty of U.S. Pat. No. 4,986,995 is that at the cooking step of rice the amount of oxygen present reduced by adding inert gas to 4-12 mol oxygen/100 g rice. This the colouration can be prevented. According to the patent in case of higher oxygen values brown coloration appears on the product.
U.S. Pat. No. 6,082,251 introduces a procedure and a machine for cooking food, and amongst them rice. The patent mainly describes the equipment used for cooking which is divided into several zones or chambers. The procedure consists of more steps. After the usual soaking the moisture content of rice is adjusted to 50-65 m % in the cooking zone of the equipment. After that rice is washed with 25° C. water and pre-steamed; soaked in 80° C. water for 15 minutes and then steamed on atmospheric pressure for 15 minutes. The drying of rice is done in three separate zones of the machine on 250 and 195° C. The procedure is capable of making parboiling rice as well.
U.S. Pat. No. 4,649,055 introduces a procedure to make parboiling dried rice. The soaking of rice is done on 65° C. on 5 pH, in a mildly acidic agent for 15 minutes. After filtering cooking and steaming is done on atmospheric pressure on 100° C. for 10 minutes. After that with several stirring rice is let to rest on 5 pH for a short time and then dried. At the cooking step it is very important that the moisture content of rice is over 60 m %, because—according to the patent—the colouration of rice can be prevented by that.
One of the modified versions of above presented procedures is U.S. Pat. No. 4,927,660, which also describes the manufacturing process of quick cooking rice. As per the patent rice which contains a certain amount of barley, bean or vegetables is swollen in the presence of additives, e.g. ethyl-alcohol. The substance of the product is excellent, no sticking of the grains is experienced. The patent skips the step of soaking and instead of that rice is treated with watery alcohol and put forth to market in vacuum packing. Because of the alcohol content the product can be stored well in spite of its high water content (40 m %). According to U.S. Pat. No. 4,921,718 soaking is done in a watery alcoholic solution, because quality reducing polluting materials like bran left-overs, oils, sugar and protein remains can be removed with this. Brown rice is first cleaned, washed, then unnecessary water is removed and soaking for 10-60 minutes follows it. Soaking is carried out in ethyl-alcohol containing water. After cooking rice is packed in an inert gas agent.
Hungarian patent no. P9903220 is also about making quick cooking rice. The basis of the procedure is that rice which has more than 17-32 m % moisture content is mechanically manipulated, hulled wet and thus bran is removed. Wet hulling results good eating quality rice.
Hungarian patent P9500519 is about the production of half cooked rice, which is free from the Maillard effect brown. According to the patent the favourable colour is reached without using additives.
You can produce short cooking time rice partly different from the classic precooking method. The soaking step is intensified, by alternating heating and cooling, thus rice absorbs 15-20 m % more water than its own weight (U.S. Pat. Nos. 5,550,242 and 5,591,475). This state is preserved with freezing where the gelatinization has not started yet. The product is ready to eat in 3-5 minutes with heating without water.
Instant, Ready to Eat Rice
The development of ready to eat rice was supposed to eliminate the kitchen technique disadvantages of raw rice and parboiling rice. The essential point is the following: raw rice or parboiling rice is completely cooked maybe seasoned as well, and after freezing it is put to market. This product type is ready to eat after a simple preheating. However, besides the advantages, important disadvantages also have to be taken into consideration. One disadvantage is that during production, delivery, and storing freezing is needed all the time, which means a significant energy demand and makes the product more expensive. As our invention does, not refer to the making of ready to eat rice, we do not review the related literature.
From the above you can see that the speeding up of cooking rice, thus the production of precooked or quick rice have been occupying researchers for a long time and the literature of achieved results is very large.
Ready to eat and quick rice needs water, energy and several procedures, in spite of the fact that procedure parameters were already optimized.
Further disadvantages of the introduced technologies are the following:                Precooking is basically a hydrothermal treatment thus the dissolution of soluble components from the grains (e.g. starch, protein, etc.) is unavoidable.        Because of the high moisture content which is adjusted with soaking (35-60 m %) and because of the steaming heat treatment tension occurs in the inside of the grain which results in cracks and in the breaking of the product. It is also a consequence of multiple-stage manipulation (mechanic surface moisture removal, final drying).        
Summarizing the procedures on making parboiling or quick cooking rice it can be stated generally, that the following steps are part of each process with smaller or bigger differences:
The manufacturing procedures used for pretreatment consist of the main steps below:                Soaking: usually between 50-70° C., in 6-16 excess water for 2-6 hours, when the moisture content of rice increases to 30-40 m %.        Water removal, resting: the removing of unnecessary water is carried out mechanically for example by spinning. During rest time moisture content evenly spreads in the whole grain.        Heat treatment: usually cooking on 95-105° C. for 10-20 minutes, during which the gelatinization of partly crystal endosperm (starch) starts.        Drying: the heat treated and high moisture content rice grains are treated with hot air until moisture content reach the required 14 m %.        
The above, generally use manufacturing procedures can be divided into three groups on basis of the heat treatment:                Steaming method: every step of the procedure is carried out on atmospheric pressure, heat transmission is done by steaming.        Dry-heat method: heat transmission is carried out by dry air, using non-watery liquid or hot sand. Microwave technique can be placed into this procedure group as a heat transmission procedure using pure energy.        Pressure steaming method: instead of soaking only humidifying is used and the steaming is done under pressure.        
The common characteristic and at the same time disadvantage of the earlier presented parboiling or quick cooking rice making procedures is that the final product is only ready after numerous steps and a great amount of water is needed to reach the required gelatinization. This water has to be removed after the heat treatment and the moisture content needs to be reduced to 12-14 m %, in order to have a microbiologically stable, non perishable rice.